Hall of Fame - Arthur Humes (3)

Harpacticoids or how it All Started

Arthur's interest in associated copepods was stimulated by the discovery of a new harpacticoid in the gill chamber of marsh crabs when he was studying their nemertean parasites as part of his Ph.D. at Louisiana State University (Humes, 1941). This very first new copepod, Cancrincola plumipes, was a representative of the Ameiridae (currently classified as the family Cancrincolidae) and Arthur returned to publish on this group on several subsequent occasions when surveying terrestrial crabs along both sides of the central Atlantic. The genera Cancrincola Wilson, 1913 and Antillesia Humes, 1958 utilize primarily Gecarcinidae (true land crabs) as hosts and are restricted to the Atlantic basin. Stimulated by his initial discovery, Arthur extended his search for harpacticoids to another group of terrestrial crabs, the Grapsidae and discovered that at least in the Indo-Pacific a different genus, Pholetiscus Humes, 1947, was associated with this host group (Humes, 1956). Arthur's recognition of the canthocamptid affinities of this new genus was significant since it demonstrated that the primarily free-living Harpacticoida had entered into association with land crabs at least twice during their evolutionary history.

During his career Arthur Humes described 23 species of harpacticoids, belonging to ten different families and utilizing eight different host groups: Crustacea, Hydrozoa, Scyphozoa, Scleractinia, Alcyonacea, Bivalvia, Holothuroidea and Echinoidea. Harpacticoids have generally been considered to be only rarely associated with invertebrates but Humes' studies have firmly established that at least in the modified families Tegastidae, Peltidiidae and Porcellidiidae several lineages have entered into symbiotic relationships with cnidarians, echinoderms and hermit crabs. The latter group offers a good example of independent colonization by three different families of harpacticoids, the Tisbidae, Porcellidiidae and Canuellidae (Humes and Ho, 1968a, b).

Copepods and Cnidaria - His Lifetime Obsession

Although Arthur published on a plethora of host groups it was the Cnidaria that was to occupy him for most of his scientific career. Copepods are associated with all three classes of Cnidaria, the Hydrozoa, the Scyphozoa and the Anthozoa, and Humes published on all three of them. Humes' studies of the poecilostomatoid family Macrochironidae contributed significantly to the systematics of copepods associated with the polyp stages of hydroids (e.g. Humes, 1966, 1977; Humes and De Maria, 1969) and the scyphozoan medusae (e.g. Humes, 1969, 1970) but it is his work on the Anthozoa that deserves special mention. His first paper on this group was not until 1958 when he described a new species of Lamippe Bruzelius, 1858 from West African pennatulaceans but what followed after his fieldwork in Nosy Be' was a real deluge of new taxa, representing 251 new species associated with hexacorallian hosts and 130 new species with octocorallian hosts. Except for the Ceriantharia and the Corallimorpharia, Arthur Humes surveyed hosts of all major anthozoan groups. No copepodologist before him has dominated this field as Arthur did and we suspect none ever will again.

Among the various groups of the Hexacorallia, the Scleractinia or hard corals have more copepod associates than any other group. The vast majority of these associates belong to the Anchimolgidae, Rhynchomolgidae and Xarifiidae. Members of the Anchimolgidae are exclusively associated with scleractinian corals and are currently accommodated in 28 genera - 27 of which having been described by Humes and the remaining one being named after him by Sebastian and Pillai (1973) [Humesiella]. Arthur named no less than 84 species of Anchimolgidae which represents nearly 95% of the total number described.

The Xarifiidae is a good example of the progress stimulated by Humes' research. Xarifiids are internal parasites of both hermatypic and ahermatypic scleractinian corals and had never been reported before 1960. They inhabit the gastrovascular cavities of the coral polyps and can best be extracted using the techniques described above (Humes and Dojiri, 1982). This family had humble beginnings: in 1960 Humes described just two species, which he placed in a new genus, Xarifia, the genotype of his new family. Currently the Xarifiidae comprises 84 species in four genera and Humes is author or co-author (with either Ju-shey Ho or Masahiro Dojiri) of all four genera and the great majority (76) of the 84 species (Humes, 1960b, 1962, 1985a; Humes and Ho, 1967, 1968; Humes and Dojiri, 1982, 1983). The family is incompletely known since Humes (1985a) mentioned an additional 16 new species in his possession that were represented by too few specimens to allow their description. The distribution of xarifiids is limited by the ecological requirements of their coral hosts but they occur from the Red Sea-Madagascar area eastward to an arc formed by Japan-Enewetak Atoll-New Caledonia (Humes, 1985a). They are absent from the Caribbean and from the Pacific east of 166º W (e.g. from Hawaii, Moorea and Panama).

The Xarifiidae is a classic example of a family of associated copepods which, once their habitat was discovered and a method to extract them was developed, proved to be both widespread and common. In stark contrast is the family Vahiniidae, also associated with cnidarian hosts, in this case antipatharians, and also established by Humes (Humes, 1967). The family was based on a monotypic new genus Vahinia Humes, 1967 and a second species was added to the genus in 1979 (Humes, 1979) but, despite extensive sampling of antipatharians, more vahiniids have not been collected. The expenditure of sufficient search effort by Arthur Humes now allows us to conclude that these animals are genuinely rare.

Within the Octocorallia, the Alcyonacea or soft corals have the greatest number of copepod associates and like with the scleractinians, our knowledge on this group bears the strong stamp of Arthur Humes' approach to systematics. The first unequivocal association of a copepod with an alcyonacean was reported by Stock and Kleeton (1963) who discovered Critomolgus bulbipes (Stock and Kleeton, 1963) on two soft corals in the vicinity of Banyuls. At that time nothing was known about such associations in the tropical Indo-Pacific. However, Humes'  extensive fieldwork in Madagascar, New Caledonia, the Moluccas and Enewetak Atoll triggered a series of papers on soft coral associates and these served to demonstrate that copepods are particularly abundant on alcyonaceans and gorgonaceans. Three decades after the initial discovery of a copepod on a soft coral, 98 copepod species are now known to occur on Indo-Pacific alcyonaceans, 96 of which were described by Humes, solely or jointly with M. Dojiri, B.W. Frost, J.-s. Ho or J.H. Stock (Humes, 1990a; 1996).

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